1. Field of the Invention
This invention relates to a demulsification process. More particularly, this invention relates to a demulsification agent which is used to treat stable oil-in-water emulsions or water-in-oil emulsions formed with spent mud acids produced from wells which have undergone acidization treatments.
2. Description of the Prior Art
Acidization treatments are commonly performed in oil wells which penetrate subterranean petroleum reservoirs. In these treatments acid solutions comprising mixtures of both hydrochloric and hydrofluoric acid as well as other ingredients are injected under pressure into the subterranean reservoir in order to improve the porosity and permeability of the rock formation so as to increase the amount of petroleum that can be extracted from the well. These treatments are quite common and very effective. However, they are not without associated problems.
One of the most significant problems created by the acidization treatment is the subsequent formation of very stable oil-in-water emulsions in the produced fluids from the well. Studies have indicated that the most stable of emulsions are formed from spent mud acid and materials simulating formation fines. Less stable in order of decreasing emulsion stability are emulsions formed from spent mud acid alone, unspent mud acid, and unspent hydrochloric acid. Most commonly crude oil and formation water alone do not show significant emulsification tendencies.
The most stable emulsions were formed in conjunction with formation fines. The creation of fines by the acidization of sandstone formations with mixed hydrofluoric-hydrochloric acid is well established in the literature. Also, the ability of solid materials to stabilize emulsions is well recognized. The acidization process then seems to create formation fines by a partial disintegration of the formation matrix. The fines so created are somehow made partially oil wet in the acidization process and, because of this mixed wettability, are capable of stabilizing emulsions of many types of crude oils and produced water.
These stable emulsions are not susceptible to conventional oil field demulsification methods such as the treatment of the produced fluids in settling tanks and heater treaters even in conjunction with conventional demulsification agents.
Handling of these stable emulsions presents a particular problem in centralized produced fluids treatment facilities which process the production from a great number of wells by continuous separation of the combined produced fluids into clean oil and water streams. Introduction of these stable emulsions into this type of treatment facility can cause massive upsets. When these facilities become filled with emulsions, the result is either curtailment of production from the producing wells or introduction of wet oil into the crude oil pipelines leaving the treatment facility.
Curtailment of production has several adverse consequences. Not only is production lost during the period of curtailment, but often a certain percentage of the wells will sand up or fail to return to production after being shut in. Thus, the immediate loss of current production is only a part of the economic loss. The cost of workovers and in some cases, permanent loss of producing capacity is often a more significant cost of such curtailments. Shipping of wet oil from the treatment plant through the outlet crude oil pipeline is also an unattractive alternative. Commonly the downstream users of the crude oil stream are not prepared to handle high water levels within the crude oil stream and severe upsets will occur in their facilities as well.
Two different methods have been disclosed to deal with the problems created by the presence of these stable emulsions resulting from acid stimulation treatments in these wells. One method is to isolate the produced fluids from the treated well until such time as the stable emulsions are no longer being produced from the well. Such isolated fluids are then treated separately. Another method is to introduce an effective demulsification agent which will specifically combat the stable emulsions formed by the spent mud acids and formations finds either into the acid treatment solution as it is injected into the well initially or to introduce this same demulsifier into the produced fluid stream from the acidized well.